Disregard skip options for streamed files

[ashbreeze]

skip_gitignore is kinda slow, but it's much faster than having to process all files in the repo. At least when I'm processing multiple files at once.

During daily development, I use the vscode "Sort Imports" feature, which internally streams the contents of the file to isort. In this case, it is unbearably slow:

$ time echo 123 | isort - --filename=/code/foobar.py
123

real    0m0.195s
user    0m0.089s
sys     0m0.025s

$ time echo 123 | isort - --filename=/code/foobar.py --gitignore
123

real    0m7.326s
user    0m3.382s
sys     0m1.737s

That's 37 times slower.

If we're streaming in data, it probably makes sense to just disregard all skip conditions.